1. Field of the Invention
The present general inventive concept relates to a hard disk drive, and more particularly, to a hard disk drive including a head stack assembly (HSA) having reduced off-track.
2. Description of the Related Art
A hard disk drive is an auxiliary memory device used in computers, MP3 players, or mobile phones that reads data stored in a disk. During operation of the hard disk drive, the head slider floats a predetermined distance above the disk and reads the data stored in the disk, or writes data into the disk, by using a magnetic head in the head slider to reproduce the data. A head stack assembly supports the head slider which is mounted on a front edge thereof and moves the head slider to a predetermined position on the disk.
When the hard disk drive is physically disturbed or when the head stack assembly accidentally vibrates, the magnetic head may skip from a certain track. A situation in which the magnetic head skips from the track it is supposed to be reading from or writing to is referred to as off-track.
FIG. 1 is a diagram illustrating an off-track caused by disk vibration.
Referring to FIG. 1, when a writing or reading operation is performed, the magnetic head 127(d0) on the head slider 27 and a certain track T(d0) located on a concentric circle about the center of the disk 10 may both be located on a vertical line VL. Since the magnetic head 127(d0) and the track T(d0) are located along the same plane in a horizontal direction at this time, off-track of the head slider 27, or more specifically, of the magnetic head 127(d0), is 0. When the hard disk drive vibrates, an outer circumference of the disk 10 and the head slider 27 of the head stack assembly vibrate in a vertical direction to cause the magnetic head 127 to move off-track. In particular, when the disk 10 and the head slider 27 vibrate downward, a track T(d1) moves toward the outer circumference of the disk 10 while the magnetic head 127(d1) moves toward the center of the disk 10, causing the magnetic head 127 to move off-track.
In the above example, the element label 127(d0) indicates that the magnetic head 127 is located at a certain distance from the center of the disk 10 in a resting state (d0). When the disk 10 vibrates downward, the magnetic head 127 moves a distance from the center of the disk 10 and is in a first vibration state (d1). The track T(d1) may move due to slight amounts of flexion or expansion of the disk 10 during vibration, for example.
On the other hand, when the disk 10 and the head slider 27 vibrate upward, a track T(d2) moves toward the center of the disk 10 while the magnetic head 127(d2) moves toward the outer circumference of the disk 10, so that the magnetic head is forced off-track. Movement of the track T(d2) may be caused by a slight compression of the disk surface during vibration, for example. A positioning error signal (PES) caused by the off-track adversely affects reliability of data writing/reading qualities of the hard disk drive.